Determination of an Active Substance, Alcacyl - METTLER TOLEDO

Determination of an Active Substance, Alcacyl

SampleCalcium carbasalate

Calcium carbasalate (calcium salt of acetylsalicylic acid = Ca-ASA) in Alcacyl

 

Application

Analgesic

 

Conditions

Measuring cellsDSC820 or TGA850

Pan: Aluminum 40 µl or 100 µl, with pierced lid

Sample preparation: As received, no preparation

DSC measurement: Heating from 30 °C to 300 °C at 10 K/min

TGA measurement: Heating from 30 °C to 300 °C at 10 K/min

Atmosphere: Nitrogen, DSC: 50 cm3/min, TGA: 80 cm3/min

 

 

Interpretation

The active ingredient can be detected with DSC and the melting point and the heat of fusion can be measured. This assumes, however, that the pure substance is available for reference purposes. Analysis is possible using the tablet’s weight and information from the manufacturer, provided that no interaction occurs between the active and inactive ingredients.

The TGA curve of Alcacyl shows two steps whereas that of Ca-ASA just one. A comparison of the second step of Alcacyl (= -24%) with the decomposition step of Ca-ASA (= -49%), shows that the weight loss corresponds almost exactly to the loss expected by decomposition of the active substance.

 

Evaluation

Since the samples decompose on melting, the integration of DSC peak is performed using the baseline type ‘horizontal left’.

DSCOnset, °CΔH, J/g
Ca-Carbasalte203.9133.5
Alcacyl203.028.2

 

TGAStep 1, %Step 2, % (decomposition)
Ca-Carbasalte-49.0
Alcacyl5.124.3

 

The mean value of the weight of 8 tablets was 1.09008 g and the Ca-Carbasalate content was 528 mg. This corresponds to a value of 48.4% for the content of the active ingredient.

For the DSC analysis of Alcacyl a heat change of 51.6 J/g (107.3 J/g x 0.484 = 51.6 J/g) is expected for the active ingredient content of 48.8%.

For the TGA analysis the step should correspond to about 23.7 % (49% weight loss of the Ca-Carbasalate x active ingredient content 0.484 = 23.7%).

While the TGA results agree with the values expected, this is not the case with the DSC measurement. The reason here is the difficulty of clearly separating the melting peak from the decomposition peak.

 

Conclusion

An analysis of the active ingredient is in principle possible, provided that no interaction occurs between the active and the inactive ingredients of the tablet. The content can also be estimated using the heat of fusion. In this case the TGA is the more accurate method, since the decomposition process that occurs at the same time interferes with the DSC analysis.

 

Determination of an Active Substance, Alcacyl | Thermal Analysis Application No. HB803 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals